<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        h4 {
            color: red;
        }

        #d1 {
            width: 100px;
            height: 100px;
            background-color: cyan;
        }

        .msg {
            color: white;
        }
        .error {
            background-color: red;
        }
        .success {
            background-color: green;
        }

        #d1:hover {
            background-color: orange;
        }

        h4,#d1,.error {
            border: 5px solid black;
        }

        a:link{color: grey}
        a:visited{color: green}
        a:hover{color: orange}
        a:active{color: red}

        input[name="uname"] {
            background-color: yellow;
        }

        * {
            font-style: italic;
        }

        #d2 span {
            background-color: pink;
        }

        #d2>div>span {
            color: green;
        }

    </style>
</head>
<body>
    <div id="d1">我是div</div>
    <div>我是div</div>
    <div>我是div</div>

    <p>我是段落</p>
    <h4>我是标题</h4>
    <h4>我是标题</h4>
    <hr>

    <span class="error msg">用户名不能为空！</span>
    <span class="error msg">密码不一致！</span>
    <span class="error msg">身份验证失败！</span>
    <span class="success msg">手机号格式正确</span>
    <span class="success msg">邮箱格式正确</span>
    <hr>

    <a href="https://www.baidu.com">超链接1</a>
    <a href="abc">超链接2</a>
    <hr>

    <input type="text" name="uname">
    <input type="text" name="nickname">
    <select name="uname">
        <option value="1"></option>
        <option value="2"></option>
    </select>
    <hr>
    <div>
        <span>111</span>
        <div>
            <span>222</span>
            <p>测试文字</p>
            <p>我是<span>333</span>段落</p>
        </div>
        <span>444</span>
    </div>

</body>
</html>